This invention relates to television, and more particularly, to a high definition television broadcast system.
Advances in technology that have taken place since television was first broadcast nearly 50 years ago can provide a much higher quality television picture than is provided by currently available systems, and this coupled with changes in social environment and diversification of human consciousness, have created a demand for a new television system capable of providing richer information to the home viewer. High definition television (HDTV) requires high horizontal and vertical resolutions, a wide image aspect ratio, and high fidelity stereophonic sound, which desirably are achieved within the constraints of channel bandwidth and noise, compatibility with existing systems, receiver cost and psycho-visual needs. High vertical resolution calls for more scan lines than the 525 presently in use in North America and Japan. Japan Broadcasting Company (NHK) has proposed a high definition system with 1125 lines, 30 frames/sec (60 fields/sec), and 20 MHz luminance band width. Of the 1125 lines, 80 are in the vertical blanking interval, leaving 1045 displayable lines. Having determined from extensive tests that viewers prefer a wide screen similar to feature films, the aspect ratio (width to height) is 5:3 instead of the 4:3 of ordinary television.
Although the images provided by NHK's experimental system are impressive, far better than traditional television pictures by virtue of containing about eight times more information, its total baseband video band width of 30 MHz makes it more suitable for production than broadcasting. Any HDTV system should provide for conversion to existing standards, as by reading out an HDTV frame store at lower resolution and differing framing rates. However, the 1125 lines of the NHK system bear no simple relationship to the 525-line raster of the NTSC system, and, moreover, its field rate of exactly 60 Hz is unlike every other existing broadcast system; the NTSC system used in North America and Japan runs at 59.94 Hz to avoid a sound interference problem caused by 60 Hz operation.
A primary object of the present invention is to provide an improved HDTV broadcast system that will be readily convertible to the existing 525-line NTSC system.
Another object of the present invention is to provide an HDTV broadcast system that will be compatible with a time multiplexed component (TMC) broadcast and thus compatible with NTSC receivers using a component-to-NTSC converter.
Another object of the invention is to provide a dual standard television broadcast system in which compatible 525-line picture signals are broadcast on one channel and an augmentation signal is broadcast on a second channel to produce 1050-line, wide-screen HDTV pictures.